The present invention relates to a high-quality titanium target for sputtering, in which impurities content is reduced, and which can prevent occurrence of cracking and breaking even in high-power sputtering (high-rate sputtering), stabilize sputtering characteristics, and effectively suppress occurrence of particles in formation of a film. Note that throughout the description, impurity concentrations are all expressed by mass %.
In recent years, various electronic instruments have been developed originated from a significant progress of semiconductors, and improvements in performance of the instruments and development of novel instruments are being performed daily and hourly.
In such a circumstance, there is a tendency that electronic and device instruments are further reduced in size and are increased in degree of integration. A large number of thin films are formed in various steps of producing these instruments, and titanium is also utilized due to the specific metallic properties thereof in formation of thin films of many electronic instruments as, for example, titanium films or its alloy films, titanium silicide films, or titanium nitride films.
In the case of forming such thin films of titanium (including alloys and compounds of titanium), it should be paid attention that titanium itself is required to have a significantly high purity.
Thin films used in, for example, semiconductors tend to be further reduced in thickness and size, the distances between each film are extremely short, and the integration density is increasing. This causes a problem that the material constituting a thin film or impurities contained in the thin film diffuse to the adjacent thin film. Accordingly, the constitutive material balance between a thin film and its adjacent film is collapsed to cause a severe problem to decrease the function that should be essentially possessed by the film.
In the process of producing such a thin film, the film is heated to several hundred degrees (Celsius) in some cases, and the temperature also rises during the use of an electronic instrument in which a semiconductor device is integrated. Such a rise in temperature further increases the diffusion rate of the aforementioned material to cause a severe problem of functional depression in the electronic instrument by the diffusion. In general, for example, films of titanium, its alloy, titanium silicide, or titanium nitride can be formed by physical vapor deposition such as sputtering or vacuum vapor deposition. Sputtering, which is most widely used among these methods, will be described below.
The sputtering is a method of allowing positive ions such as Ar+ to physically collide with a target disposed on the cathode to release metal atoms constituting the target by the collision energy. A nitride can be formed by sputtering using titanium or its alloy (e.g., a TiAl alloy) as a target in an atmosphere of a gas mixture of argon gas and nitrogen.
In formation of this sputtering film, if the titanium (including alloys and compounds) target contains impurities, coarse grains floating in a sputtering chamber adhere onto a substrate to cause disconnection or short-circuit of a thin film circuit, and the occurrence of particles, which may cause to form protrusions on the film, increases so that a problem occurs that uniform films cannot be formed.
Because of this, it is obviously necessary to reduce the amounts of transition metals, high melting metals, alkali metals, alkali earth metals, and other metals, which are conventionally recognized as impurities. Unfortunately, even if these elements are reduced as much as possible, the aforementioned particles occur. Thus, no fundamental solution has been found yet.
In addition, though a titanium thin film may be used as a pasting layer for preventing occurrence of particles when forming a titanium nitride (Ti—N) film, the titanium thin film is hard and cannot have a sufficient strength of adhesion, resulting in peeling off the inner wall or a component of a film formation apparatus. Thus, the titanium thin film does not achieve the function as a pasting layer and causes occurrence of particles.
Furthermore, recently, there is a demand for high-rate sputtering (high-power sputtering) in order to increase the production efficiency. In such sputtering, cracking or breaking of the target tends to occur, and it causes a problem of preventing stable sputtering. Patent Documents 1 and 2 are cited as prior art documents.
Patent Document 3 describes a titanium target for sputtering showing an X-ray diffraction intensity ratio of (0002)/(10−11)≧0.8 and (0002)/(10−10)≧6 on the sputtered surface and having a recrystallized structure with an average crystal grain size of 20 μm or less, and proposes a titanium target, with which a film can be easily formed in a narrow and deep contact hole and occurrence of particles can be reduced.
Patent Document 4 describes a titanium target for sputtering having a Vickers hardness in the range of 110≦HV≦130 and a recrystallized structure, and proposes a titanium target, with which sputtered grains are arranged in the same direction, a film can be easily formed in a narrow and deep contact hole, and occurrence of particles can be reduced.
Patent Document 5 describes a titanium target for sputtering where a titanium target material having a recrystallized structure with a maximum grain size of 20 μm or less and an average crystal grain size of 10 μm or less is diffusion-bonded to a backing plate primarily made of aluminum, and proposes a titanium target, with which sputtered grains are arranged in the same direction, a film can be easily formed in a narrow and deep contact hole, and occurrence of particles can be reduced.
In the inventions proposed in the aforementioned documents, however, cracking or breaking readily occurs during high-power sputtering, and it is thought that the problems described in each document are not sufficiently solved.    Patent Document 1: International Publication No. WO 01/038598    Patent Document 2: Published Japanese Translation No. 2001-509548 of PCT Application    Patent Document 3: Japanese Laid-Open Patent Publication No. H8-269701    Patent Document 4: Japanese Laid-Open Patent Publication No. H9-104972    Patent Document 5: Japanese Laid-Open Patent Publication No. H9-143704